Piezoelectric transformer

ABSTRACT

A piezoelectric transformer that includes a piezoelectric body having driving portions and a power generating portion, an input electrode, and an output electrode. The driving portions and the power generating portion are arranged in the lengthwise direction of the piezoelectric body. The driving portions are disposed symmetrically relative to a plane that passes through a center of the piezoelectric body in the lengthwise direction and is orthogonal to the lengthwise direction, occupy no less than half of the regions in the piezoelectric body, and are include two or more adjacent polarized regions.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International applicationNo. PCT/JP2013/069151, filed Jul. 12, 2013, which claims priority toJapanese Patent Application No. 2012-248894, filed Nov. 13, 2012, theentire contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to piezoelectric transformers, andparticularly relates to piezoelectric transformers used in contactlesspower transmission.

BACKGROUND OF THE INVENTION

Contactless power transmission is recently being used as a method forcharging secondary batteries in cellular phones, digital cameras, andthe like. Electric field coupling, in which power is transmitted throughcapacitive coupling between opposing electrodes, is one technique usedfor contactless power transmission. In contactless power transmissionthat uses electric field coupling, high voltages and high frequenciesare important for increasing the efficiency of power transmission. Assuch, in order to employ electric field coupling contactless powertransmission for electronic devices such as cellular phones, it isnecessary to provide, in an electronic device serving as a receivingside, a transformer that transforms high-voltage power supplied from asending side through contactless power transmission into low-voltagepower suited to the circuitry of the electronic device.

A piezoelectric transformer is an example of a transformer that can beused as a transformer for contactless power transmission. Thepiezoelectric transformers disclosed in Patent Document 1 and PatentDocument 2 are known as examples of conventional piezoelectrictransformers. However, the piezoelectric transformers disclosed inPatent Document 1 and Patent Document 2 are piezoelectric transformersfor cold-cathode tubes used in liquid crystal display backlights. Acold-cathode tube piezoelectric transformer handles lower frequenciesthan the frequencies demanded from transformers used for contactlesspower transmission. Accordingly, the piezoelectric transformersdisclosed in Patent Document 1 and Patent Document 2 cannot be usedas-is as transformers for contactless power transmission. Specifically,there are two ways in which the piezoelectric transformers disclosed inPatent Document 1 and Patent Document 2 can be altered to handle thehigh frequencies demanded from transformers for contactless powertransmission. One is by further reducing the size of the piezoelectrictransformer, and the other is by changing the vibration mode to ahigher-order vibration mode. With the former, further reducing the sizeof the piezoelectric transformers disclosed in Patent Document 1 andPatent Document 2 reduces the efficiency of power transmission.Accordingly, it is necessary to change the vibration mode to ahigher-order vibration mode in order to handle the high frequenciesdemanded from transformers for contactless power transmission without adrop in the efficiency of power transmission. A coil transformer isanother example, aside from a piezoelectric transformer, of atransformer that can be used as a transformer for contactless powertransmission. While coil transformers are currently the mainstream interms of transformers for contactless power transmission, they are alsolarger than piezoelectric transformers. Coil transformers furthermorecarry a risk of increased electrical resistance as the frequency ofsupplied power rises.

For such reasons, a piezoelectric transformer that employs a high-ordervibration mode is in demand as a transformer for contactless powertransmission. A piezoelectric transformer that employs primary totertiary vibration modes will be given here as an example in order todescribe a problem with piezoelectric transformers that employhigh-order vibration modes.

A piezoelectric transformer 500 illustrated in FIG. 12 is apiezoelectric transformer that uses a primary (base) vibration mode or asecondary vibration mode. A piezoelectric transformer 600 illustrated inFIG. 13 is a piezoelectric transformer that uses a tertiary vibrationmode. FIG. 12 is a diagram illustrating a side surface of thepiezoelectric transformer 500 along with stress and displacement inrespective areas of the piezoelectric transformer 500. FIG. 13 is adiagram illustrating a side surface of the piezoelectric transformer 600along with stress and displacement in respective areas of thepiezoelectric transformer 600. The arrows in FIG. 12 and FIG. 13indicate polarization directions. A graph in (a) of FIG. 12 representsstress W1 a and displacement W1 b in the respective areas in the primaryvibration mode, and a graph in (b) of FIG. 12 represents a waveform W2 aindicating stress and W2 b indicating displacement in the respectiveareas during the secondary vibration mode. A graph in FIG. 13 representsstress W3 a and displacement W3 b in the respective areas during thetertiary vibration mode.

As shown in FIG. 12, the piezoelectric transformer 500 includes a long,plate-shaped piezoelectric body 501 configured of piezoelectricceramics, an input electrode 520, and an output electrode 530. The inputelectrode 520 is provided on two main surfaces of one side of thepiezoelectric body 501. The output electrode 530 is provided on an endsurface of the other side of the piezoelectric body 501. As shown inFIG. 12, the one side of the piezoelectric body 501 is polarized along athickness direction of the piezoelectric body 501, and the other side ofthe piezoelectric body 501 is polarized along a lengthwise direction ofthe piezoelectric body 501.

According to the piezoelectric transformer 500, when a voltage at aspecific frequency is applied to the input electrode 520, a strongmechanical vibration is produced in the piezoelectric body 501 due to aninverse piezoelectric effect. A standing wave having a half-wave lengthis produced in the piezoelectric body 501 at this time. Furthermore, thepiezoelectric transformer 500 outputs a voltage corresponding to themechanical vibrations from the output electrode 530 as a result of apiezoelectric effect.

As shown in FIG. 13, the piezoelectric transformer 600 includes a long,plate-shaped piezoelectric body 601 configured of piezoelectricceramics, input electrodes 620, and output electrodes 630. The inputelectrodes 620 are provided in a central area of two main surfaces ofthe piezoelectric body 601. The output electrodes 630 are provided onboth end surfaces of the piezoelectric body 601 in the lengthwisedirection thereof. The central area of the piezoelectric body 601 ispolarized along a thickness direction of the piezoelectric body 601, andboth end portions of the piezoelectric body 601 are polarized along thelengthwise direction of the piezoelectric body 601.

According to the piezoelectric transformer 600, when a voltage at aspecific frequency is applied to the input electrode 620, a strongmechanical vibration is produced in the piezoelectric body 601 due to aninverse piezoelectric effect. A standing wave having a 1.5 wavelength isproduced in the piezoelectric body 601 at this time. Furthermore, thepiezoelectric transformer 600 outputs a voltage corresponding to themechanical vibrations from the output electrode 630 as a result of apiezoelectric effect.

The respective waveforms shown in FIG. 12 and FIG. 13 will be comparednext. Specifically, the waveforms W1 b, W2 b, and W3 b in the respectivevibration modes will be compared, by comparing the positions of theapexes of the antinodes where the phase of the displacement waveformreaches 180°, using a point at a left end portion where the displacementis equal as a base point (phase=0°). A distance between the position ofthe apex of the antinode in the secondary vibration mode and theposition of the apex of the antinode in the tertiary vibration mode isshorter than a distance between the position of the apex of the antinodein the primary vibration mode and the position of the apex of theantinode in the secondary vibration mode. This indicates that thewavelength becomes shorter in higher-order vibration modes, and theapexes of the antinodes near the base point become closer in thedisplacement waveforms in the respective vibration modes. In otherwords, with a piezoelectric transformer that uses high-order vibrationmodes, a plurality of vibration modes having similar waveforms will bepresent together. As such, if an attempt is made to excite a desiredvibration mode in a piezoelectric transformer that uses high-ordervibration modes, it is possible that a different vibration mode having awaveform similar to the waveform of the desired vibration mode will beexcited instead. In other words, piezoelectric transformers that usehigh-order vibration modes have a problem in that unnecessary vibrationmodes occur with greater ease than in piezoelectric transformers thatuse low-order vibration modes.

Patent Document 1: Japanese Patent No. 2998717

Patent Document 2: Japanese Patent No. 4297388

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide apiezoelectric transformer capable of suppressing the occurrence of anunnecessary vibration mode.

A piezoelectric transformer according to the present invention is apiezoelectric transformer that uses a seventh-order or greater vibrationmode, and includes a piezoelectric body, having a plurality of polarizedregions, that has a plurality of driving portions configured by a firstpolarized region of the plurality of polarized regions and a powergenerating portion configured by a second polarized region of theplurality of polarized regions; an input electrode that applies avoltage to each of the plurality of driving portions; and an outputelectrode that outputs a voltage generated by the power generatingportion. Here, the plurality of driving portions and the powergenerating portion are arranged in a lengthwise direction of thepiezoelectric body; the plurality of driving portions are disposedsymmetrically relative to a plane that passes through a center of thepiezoelectric body in the lengthwise direction and is orthogonal to thelengthwise direction, and occupy half or more of the regions in thepiezoelectric body; and each of the plurality of driving portions isconfigured by two or more adjacent polarized regions.

The piezoelectric transformer according to the present invention cansuppress an unnecessary vibration mode from being produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a piezoelectric transformeraccording to an embodiment of the present invention.

FIG. 2 is a cross-sectional view from an A-A cross-section in FIG. 1.

FIG. 3 is a diagram illustrating a polarization direction anddisplacement at respective areas of a piezoelectric transformeraccording to an embodiment of the present invention.

FIG. 4 is a diagram illustrating displacement at respective areas in asixth-order vibration mode and a seventh-order vibration mode.

FIG. 5 is a diagram illustrating displacement at respective areas in asixth-order vibration mode.

FIG. 6 is a diagram illustrating displacement at respective areas in aneighth-order vibration mode.

FIG. 7 is a diagram illustrating displacement at respective areas in aseventh-order vibration mode and an eighth-order vibration mode.

FIG. 8 is a diagram illustrating displacement at respective areas in aseventh-order vibration mode and a ninth-order vibration mode.

FIG. 9 is an external perspective view of a piezoelectric transformeraccording to a first variation.

FIG. 10 is an external perspective view of a piezoelectric transformeraccording to a second variation.

FIG. 11 is an external perspective view of a piezoelectric transformeraccording to a third variation.

FIG. 12 is a diagram illustrating a side surface of a piezoelectrictransformer along with stress and displacement in respective areas ofthe piezoelectric transformer, according to a comparative example.

FIG. 13 is a diagram illustrating a side surface of a piezoelectrictransformer along with stress and displacement in respective areas ofthe piezoelectric transformer, according to a comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A piezoelectric transformer and a manufacturing method thereof accordingto an embodiment of the present invention will be described hereinafter.

(Configuration of Piezoelectric Transformer)

Hereinafter, the configuration of the piezoelectric transformeraccording to this embodiment of the present invention will be describedwith reference to the drawings. FIG. 1 is an external perspective viewof a piezoelectric transformer 10 according to this embodiment of thepresent invention. FIG. 2 is a cross-sectional view from an A-Across-section in FIG. 1. FIG. 3 is a diagram illustrating a polarizationdirection and displacement at respective areas of the piezoelectrictransformer 10 according to this embodiment of the present invention.The arrows in FIG. 3 indicate the polarization directions. A lengthwisedirection of the piezoelectric transformer 10 will be defined as anx-axis direction, and directions orthogonal thereto will be defined as ay-axis direction and a z-axis direction. Note that the x axis, the yaxis, and the z axis are orthogonal to one another.

As shown in FIG. 1, the piezoelectric transformer 10 has aparallelepiped shape. The piezoelectric transformer 10 is a step-downpiezoelectric transformer that includes a piezoelectric body 20, inputelectrodes 30 and 32, an output electrode 40, and a ground electrode 50.

As shown in FIG. 1, the piezoelectric body 20 has a parallelepipedshape. The piezoelectric body 20 has a square cross-sectional shape whenviewed as a cross-section parallel to a plane containing the y axis andthe z axis. Furthermore, the piezoelectric body 20 is divided along thex-axis direction into seven equal polarized regions, as shown in FIG. 3.The polarized regions of the piezoelectric body 20 are indicated aspolarized regions 21-27, and the polarized regions are arranged in thatorder from a negative x-axis direction side toward a positive x-axisdirection side. Although the piezoelectric body 20 is configured ofPZT-based piezoelectric ceramics in the present embodiment, it should benoted that the piezoelectric body 20 may be configured of lead titanate,for example.

The polarized regions 21 and 22 are polarized in a direction parallel tothe x-axis direction, as indicated by the arrows in FIG. 3. Apolarization direction 21 d of the polarized region 21 and apolarization direction 22 d of the polarized region 22, which areadjacent to each other, are opposite from each other. Specifically, thepolarization direction 21 d faces the negative x-axis direction side,and the polarization direction 22 d faces the positive x-axis directionside. The polarized regions 21 and 22 configure a first polarizedregion.

The polarized regions 23-25 are polarized in a direction parallel to thez-axis direction, as indicated by the arrows in FIG. 3. A polarizationdirection 23 d of the polarized region 23 and a polarization direction24 d of the polarized region 24, which are adjacent to each other, areopposite from each other. Furthermore, the polarization direction 24 dof the polarized region 24 and a polarization direction 25 d of thepolarized region 25, which are adjacent to each other, are opposite fromeach other. Specifically, the polarization directions 23 d and 25 d facea positive z-axis direction side, and the polarization direction 24 dfaces a negative z-axis direction side. The polarized regions 23-25configure a second polarized region.

The polarized regions 26 and 27 are polarized in a direction parallel tothe x-axis direction, as indicated by the arrows in FIG. 3. Apolarization direction 26 d of the polarized region 26 and apolarization direction 27 d of the polarized region 27, which areadjacent to each other, are opposite from each other. Specifically, thepolarization direction 26 d faces the negative x-axis direction side,and the polarization direction 27 d faces the positive x-axis directionside. The polarized regions 26 and 27 configure the first polarizedregion. Note that the polarized regions 21-27, in which the polarizationdirections of mutually-adjacent polarized regions are opposite from eachother, are formed by carrying out a poling treatment upon having formedpolarization electrodes (not shown) between the mutually-adjacentpolarized regions.

As shown in FIG. 1, the input electrodes 30 and 32 are electrodes thatare provided at both end portions of the piezoelectric body 20 in thex-axis direction, and are configured of a metal such as Au, Ag, Pd, Cu,an alloy containing those metals, or the like. Specifically, the inputelectrode 30 is provided so as to cover an end portion of thepiezoelectric body 20 on the negative x-axis direction side thereof.Meanwhile, the input electrode 32 is provided so as to cover an endportion of the piezoelectric body 20 on the positive x-axis directionside thereof. Accordingly, the input electrodes 30 and 32 haverectangular shapes when viewed from the x-axis direction. Note that theinput electrodes 30 and 32 are electrically connected to an AC powersource.

The output electrode 40 includes an output outer electrode 42 and outputinner electrodes 441-44 n. As shown in FIG. 2, the output outerelectrode 42 is provided so as to cover respective surfaces of thepolarized regions 23-25 on a positive y-axis direction side and thepositive z-axis direction side thereof.

Meanwhile, each of the output inner electrodes 441-44 n is provided soas to span across the polarized regions 23-25 within the piezoelectricbody 20. Furthermore, the output inner electrodes 441-44 n arerectangular plates that are orthogonal to the z-axis direction, and asshown in FIG. 2, are provided in multiple in that order from thepositive z-axis direction side toward the negative z-axis directionside. Each of the output inner electrodes 441-44 n is electricallyconnected to the output outer electrode 42. Note that the outputelectrode 40 is configured of a metal such as Au, Ag, Pd, Cu, an alloycontaining those metals, or the like.

The ground electrode 50 includes a ground outer electrode 52 and groundinner electrodes 541-54 n. As shown in FIG. 2, the ground outerelectrode 52 is provided so as to cover respective surfaces of thepolarized regions 23-25 on a negative y-axis direction side and thenegative z-axis direction side thereof.

Meanwhile, each of the ground inner electrodes 541-54 n is provided soas to span across the polarized regions 23-25 within the piezoelectricbody 20. Furthermore, the ground inner electrodes 541-54 n arerectangular plates that are orthogonal to the z-axis direction, and asshown in FIG. 2, are provided in multiple in that order from thepositive side of the z-axis direction toward the negative side of thez-axis direction. Each of the ground inner electrodes 541-54 n iselectrically connected to the ground outer electrode 52. Note that theground electrode 50 is configured of a metal such as Au, Ag, Pd, Cu, analloy containing those metals, or the like.

According to the piezoelectric transformer 10 configured as describedthus far, when a voltage at a frequency corresponding to a seventh-ordervibration mode is applied to a segment sandwiched between the inputelectrode 30 and the ground electrode 50, or in other words, to thepolarized regions 21 and 22, lengthwise vibrations parallel to thex-axis direction are produced in the piezoelectric body 20 due to aninverse piezoelectric effect. In other words, the polarized regions 21and 22 serve as a driving portion in the piezoelectric transformer 10.Here, the driving portion configured by the polarized regions 21 and 22will be referred to as a driving portion 60.

Furthermore, according to the piezoelectric transformer 10, when avoltage at a frequency corresponding to the seventh-order vibration modeis applied to the polarized regions 21 and 22, a voltage at a frequencycorresponding to the seventh-order vibration mode is also applied to asegment sandwiched between the input electrode 32 and the groundelectrode 50, or in other words, to the polarized regions 26 and 27, atthe same time, which produces lengthwise vibrations parallel to thex-axis direction in the piezoelectric body 20. In other words, thepolarized regions 26 and 27 also serve as a driving portion in thepiezoelectric transformer 10. Here, the driving portion configured bythe polarized regions 26 and 27 will be referred to as a driving portion62.

As described above, the piezoelectric body 20 includes the two drivingportions 60 and 62. Furthermore, as shown in FIG. 3, the drivingportions 60 and 62 are disposed symmetrically relative to a plane S1that passes through the center of the piezoelectric body 20 in thex-axis direction and is orthogonal to the x axis. Meanwhile, the drivingportions 60 and 62 include the four polarized regions 21, 22, 26, and27, which correspond to no less than half of the seven polarized regionsinto which the piezoelectric body 20 is divided equally. Furthermore,the driving portion 60 is configured of the two adjacent polarizedregions 21 and 22, whereas the driving portion 62 is configured of thetwo adjacent polarized regions 26 and 27.

According to the piezoelectric transformer 10, the aforementionedvibrations in the piezoelectric body 20 are converted into electricalenergy in the polarized regions 23-25 due to a piezoelectric effect.This electrical energy is obtained from the output electrode 40 and issupplied to electronic components electrically connected to the outputelectrode 40. Here, a power generating portion configured by thepolarized regions 23-25 will be referred to as a power generatingportion 70.

Note that in the piezoelectric transformer 10, a surface area over whichthe input electrodes 30 and 32 and the ground electrode 50 oppose eachother is smaller than a surface area over which the output electrode 40and the ground electrode 50 oppose each other. Furthermore, a distancebetween the respective input electrodes 30 and 32 and the groundelectrode 50 is greater than a distance between the output electrode 40and the ground electrode 50. Accordingly, an electrostatic capacitybetween the input electrode 30 and the ground electrode 50 and anelectrostatic capacity between the input electrode 32 and the groundelectrode 50 are sufficiently lower than an electrostatic capacitybetween the output electrode 40 and the ground electrode 50.Accordingly, the piezoelectric transformer 10 is used as a step-downpiezoelectric transformer.

(Method for Manufacturing Piezoelectric Transformer)

First, a slurry having PZT-based piezoelectric ceramic particles as itsprimary component is molded using a doctor blade in order to obtain agreen sheet.

Next, an electrode pattern that will serve as the output innerelectrodes 441-44 n and the ground inner electrodes 541-54 n is formedon a surface of the green sheet using a method such as screen printing.A plurality of the green sheets on which the electrode pattern has beenformed are then layered together and sintered. A laminated piezoelectricceramic sintered body to serve as the piezoelectric body 20 is thenobtained by cutting the sintered green sheet.

Then, a paste configured of Au, Ag, Pd, Cu, or the like is applied toboth end surfaces in the lengthwise direction of the laminatedpiezoelectric ceramic sintered body obtained in this manner and allowedto dry, forming the input electrodes 30 and 32. Furthermore, a pasteconfigured of a metal such as Au, Ag, Pd, Cu, an alloy containing thosemetals, or the like is applied to a central area of the multilayer body,or in other words, to a surface of a region where the polarized regions23-25 are to be, and the paste is then allowed to dry, forming theoutput outer electrode 42 and the ground outer electrode 52. The outputouter electrode 42 and the output inner electrodes 441-44 n areconnected and the ground outer electrode 52 and the ground innerelectrodes 541-54 n are connected at this time.

Finally, the polarized regions 21-27 are formed by carrying out a polingtreatment; the piezoelectric body 20 is obtained and the piezoelectrictransformer 10 is completed as a result.

Effects

According to the piezoelectric transformer 10 configured as describedthus far, the occurrence of unnecessary vibration modes can besuppressed for the reasons described hereinafter. FIG. 4 is a diagramillustrating displacement at respective areas in a sixth-order vibrationmode and the seventh-order vibration mode. FIG. 5 is a diagramillustrating displacement at respective areas in the sixth-ordervibration mode. FIG. 6 is a diagram illustrating displacement atrespective areas in an eighth-order vibration mode. FIG. 7 is a diagramillustrating displacement at respective areas in the seventh-ordervibration mode and the eighth-order vibration mode. FIG. 8 is a diagramillustrating displacement at respective areas in the seventh-ordervibration mode and a ninth-order vibration mode. Here, the waveforms ofthe displacement of the respective areas in the sixth-order toninth-order vibration modes are indicated by waveforms W6, W7, W8, andW9, respectively. Apexes of antinodes in the waveforms W6, W7, and W8where the phase reaches 180° are indicated by apexes x6, x7, and x8,using a point where the displacement in each waveform is equal as a basepoint (phase=0°).

As shown in FIG. 4, according to the piezoelectric transformer 10, theapex x7 and the apex x6 are close to each other near a border betweenthe polarized region 21 and the polarized region 22. In other words,vibration modes having similar waveforms are present together in thedriving portion 60. However, according to the piezoelectric transformer10, the phase of the waveform W7 advances by 180° from segment tosegment in the polarized regions, as shown in FIG. 3. Meanwhile, thephase of the waveform W6 advances by about 154° from segment to segmentin the polarized regions, as shown in FIG. 5. As a result, according tothe piezoelectric transformer 10, a phase difference between thewaveform W7 and the waveform W6 increases as the polarized regionsprogress from the base point, as indicated in FIG. 4. Ultimately, thewaveforms W6 and W7 have mutually opposite phases at an end portion ofthe piezoelectric body 20 on the positive x-axis direction side thereof.Thus in the piezoelectric transformer 10, the waveforms W6 and W7 thatare similar at the driving portion 60 are not similar at the drivingportion 62, as shown in FIG. 4. Accordingly, the waveform W7 is producedat the driving portion 62 by applying an AC voltage corresponding to theseventh-order vibration mode. As a result, the waveform W6, which is notsimilar to the waveform W7 produced at the driving portion 62, issuppressed from being produced. For this reason, the sixth-ordervibration mode is suppressed from being produced when the AC voltagecorresponding to the seventh-order vibration mode is applied at thedriving portion 62. In other words, according to the piezoelectrictransformer 10, the sixth-order vibration mode can be suppressed frombeing excited when an attempt is made to excite the seventh-ordervibration mode.

The foregoing can also be said to apply when comparing the seventh-ordervibration mode and the eighth-order vibration mode. As described above,according to the piezoelectric transformer 10, the phase of the waveformW7 advances by 180° from segment to segment in the polarized regions, asshown in FIG. 3. Meanwhile, the phase of the waveform W8 advances byabout 205° from segment to segment in the polarized regions, as shown inFIG. 6. As a result, a phase difference between the waveform W7 and thewaveform W8 increases as the polarized regions progress from the basepoint, as indicated in FIG. 7. Ultimately, the waveforms W7 and W8 havemutually opposite phases at the end portion of the piezoelectric body 20on the positive x-axis direction side thereof. Accordingly, in thepiezoelectric transformer 10, the waveforms W7 and W8 that are similarat the driving portion 60 are not similar at the driving portion 62, asshown in FIG. 7. Accordingly, the waveform W7 is produced at the drivingportion 62 by applying an AC voltage corresponding to the seventh-ordervibration mode. As a result, the waveform W8, which is not similar tothe waveform W7 produced at the driving portion 62, is suppressed frombeing produced. For this reason, the eighth-order vibration mode issuppressed from being produced when the AC voltage corresponding to theseventh-order vibration mode is applied at the driving portion 62. Inother words, according to the piezoelectric transformer 10, theeighth-order vibration mode can be suppressed from being excited when anattempt is made to excite the seventh-order vibration mode.

As described above, according to the piezoelectric transformer 10, theplurality of driving portions 60 and 62 are provided and disposedsymmetrically relative to the plane S1, as shown in FIG. 3; accordingly,similar and unnecessary vibration modes can be suppressed from beingproduced. In addition, according to the piezoelectric transformer 10,the four polarized regions 21, 22, 26, and 27, which correspond to noless than half of the equally divided seven polarized regions in thepiezoelectric body 20, forcefully restrict a stress (displacement)distribution as a result of the driving portions 60 and 62 beingconfigured. Accordingly, the piezoelectric transformer 10 suppressessimilar and unnecessary vibration modes from being produced in thedriving portions 60 and 62.

Furthermore, the driving portions 60 and 62 are provided at both endportions of the piezoelectric body 20 in the piezoelectric transformer10, as shown in FIG. 3. As shown in FIG. 4 and FIG. 7, the end portionof the piezoelectric body 20 on the positive side thereof in the x-axisdirection corresponds to a position where the waveform of an odd-ordervibration mode and the waveform of an even-order vibration mode haveopposite phases. Accordingly, even when a high-order vibration mode isexcited, the piezoelectric transformer 10 can more effectively suppressthe vibration modes of orders before and after the high-order vibrationmode from being produced.

The piezoelectric transformer 10 can suppress an odd-order vibrationmode different from the seventh-order vibration mode (for example, afifth-order vibration mode and the ninth-order vibration mode) frombeing produced. This will be described next using the ninth-ordervibration mode as an example.

As shown in FIG. 8, the apex of the antinode in the waveform W7 of theseventh-order vibration mode and the apex of the antinode in a waveformW9 of the ninth-order vibration mode match at both end portions of thepiezoelectric transformer 10. In other words, the waveform W7 and thewaveform W9 are similar at both end portions of the piezoelectrictransformer 10 (that is, at the polarized region 21 and the polarizedregion 27). However, even if the waveform W7 and the waveform W9 aresimilar at the polarized region 21, the phase of the waveform W7 and thephase of the waveform W9 shift from each other as the polarized regionsprogress from segment to segment, and thus the waveform W7 and thewaveform W9 are not similar at the polarized region 22. Likewise, evenif the waveform W7 and the waveform W9 are similar at the polarizedregion 27, the phase of the waveform W7 and the phase of the waveform W9shift from each other as the polarized regions progress from segment tosegment, and thus the waveform W7 and the waveform W9 are not similar atthe polarized region 26. Accordingly, as shown in FIG. 3, in thepiezoelectric transformer 10, the driving portion 60 is configured ofthe two adjacent polarized regions 21 and 22. Likewise, the drivingportion 62 is configured of the two adjacent polarized regions 26 and27. The waveform W7 is produced at the polarized region 21 in thedriving portion 60 and the polarized region 27 in the driving portion 62by applying an AC voltage corresponding to the seventh-order vibrationmode. As a result, the waveform W9, which is not similar to the waveformW7 produced at the polarized region 21 in the driving portion 60 and thepolarized region 27 in the driving portion 62, is suppressed from beingproduced. In other words, in the case where the desired vibration modeis of an odd order, the piezoelectric transformer 10 can suppress adifferent odd-order vibration mode from being produced. Likewise, in thecase where the desired vibration mode is of an even order, a differenteven-order vibration mode can be suppressed from being produced.

As can be seen in FIG. 1, in the piezoelectric transformer 10, thepiezoelectric body 20 has a square cross-sectional shape when viewed asa cross-section parallel to a plane containing the y axis and the zaxis. As a result, y-axis direction vibration modes and z-axis directionvibration modes are the same in the piezoelectric body 20. Thepiezoelectric body 20 therefore reduces the number of vibration modes,as compared to a case where the cross-sectional shape thereof isrectangular. In other words, the piezoelectric transformer 10 furthersuppresses unnecessary vibration modes from occurring.

As shown in FIG. 3, an electrostatic capacity is formed between theinput electrode 30 and the ground electrode 50 in the piezoelectrictransformer 10. The plurality of polarized regions 21 and 22 arefurthermore present between the input electrode 30 and the groundelectrode 50. When a plurality of polarized regions are present betweenthe input electrode 30 and the ground electrode 50, the distance betweenthe input electrode 30 and the ground electrode 50 increases as thenumber of those polarized regions rises, and as a result, theelectrostatic capacity formed between the input electrode 30 and theground electrode 50 drops. In other words, the piezoelectric transformer10 handles cases where an extremely low input electrostatic capacity isdesired. Note that the same applies to the electrostatic capacity formedbetween the input electrode 32 and the ground electrode 50.

Furthermore, as shown in FIG. 3, there is an odd number of polarizedregions in the piezoelectric transformer 10. Having an odd number ofpolarized regions results in the polarization directions beingsymmetrical relative to the plane S1, as shown in FIG. 3. Accordingly,the piezoelectric transformer 10 is not anisotropic depending on amounting direction. It is thus not necessary to specify the mountingdirection when mounting the piezoelectric transformer 10 on a board, andthus identification marks for mounting directions are not necessary.

(First Variation)

Hereinafter, a piezoelectric transformer 10-1 according to a firstvariation will be described with reference to the drawings. FIG. 9 is anexternal perspective view of the piezoelectric transformer 10-1according to the first variation. The arrows in FIG. 9 indicate thepolarization directions.

The piezoelectric transformer 10-1 is different from the piezoelectrictransformer 10 in terms of the position and shape of the outputelectrode 40, the position and shape of the ground electrode 50, and thepolarization directions of the polarized regions 23 and 25. Thepiezoelectric transformer 10-1 is the same as the piezoelectrictransformer 10 in other respects, and thus redundant descriptions willbe omitted. Note that the output electrode of the piezoelectrictransformer 10-1 is referred to as an output electrode 40-1 and theground electrode of the piezoelectric transformer 10-1 is referred to asa ground electrode 50-1. Furthermore, the polarized regions in thepiezoelectric transformer 10-1 that correspond to the polarized regions23 and 25 will be referred to as polarized regions 23-1 and 25-1. InFIG. 9, elements that are the same as those in the piezoelectrictransformer 10 are assigned the same reference signs as in thepiezoelectric transformer 10.

The polarized regions 23-1 and 25-1 are polarized in a directionparallel to the x-axis direction, as indicated by the arrows in FIG. 9.Specifically, a polarization direction 23-1 d of the polarized region23-1 faces the negative x-axis direction side. Likewise, a polarizationdirection 25-1 d of the polarized region 25-1 faces the positive x-axisdirection side.

As shown in FIG. 9, the output electrode 40-1 is provided in thepolarized region 24. The basic configuration of the inner electrodes andso on in the output electrode 40-1 is the same as in the outputelectrode 40, and thus descriptions thereof will be omitted here.

As shown in FIG. 9, the ground electrode 50-1 is provided in thepolarized region 24. The basic configuration of the inner electrodes andso on in the ground electrode 50-1 is the same as in the groundelectrode 50, and thus descriptions thereof will be omitted here.

According to the piezoelectric transformer 10-1 configured as describedthus far, the polarized region 24 functions as a power generatingportion 70-1. Meanwhile, the polarized regions 21, 22, and 23-1configure a driving portion 60-1, and the polarized regions 25-1, 26,and 27 configure a driving portion 62-1. In other words, according tothe piezoelectric transformer 10-1, a region of a piezoelectric body20-1 occupied by the driving portions is greater in size than in thepiezoelectric body 20 of the piezoelectric transformer 10. Thepiezoelectric transformer 10-1 can therefore provide a higher couplingcoefficient than the piezoelectric transformer 10.

Meanwhile, an electrostatic capacity is formed between the inputelectrode 30 and the ground electrode 50-1 in the piezoelectrictransformer 10-1. Furthermore, as shown in FIG. 9, the three polarizedregions 21, 22, and 23-1 are present between the input electrode 30 andthe ground electrode 50-1. This number of polarized regions is greaterthan the number of polarized regions between the input electrode 30 andthe ground electrode 50 in the piezoelectric transformer 10. As aresult, a distance between the input electrode 30 and the groundelectrode 50-1 in the piezoelectric transformer 10-1 is greater than thedistance between the input electrode 30 and the ground electrode 50 inthe piezoelectric transformer 10. Accordingly, the electrostaticcapacity formed between the input electrode 30 and the ground electrode50-1 in the piezoelectric transformer 10-1 is lower than theelectrostatic capacity formed between the input electrode 30 and theground electrode 50 in the piezoelectric transformer 10. In other words,the piezoelectric transformer 10-1 handles cases where an even lowerinput electrostatic capacity than the piezoelectric transformer 10 isdesired. The same applies to the electrostatic capacity formed betweenthe input electrode 32 and the ground electrode 50-1.

(Second Variation)

Hereinafter, a piezoelectric transformer 10-2 according to a secondvariation will be described with reference to the drawings. FIG. 10 isan external perspective view of the piezoelectric transformer 10-2according to the second variation, and is a diagram that alsoillustrates polarization directions and displacement at respectiveareas. The arrows in FIG. 10 indicate the polarization directions. Notethat descriptions of configurations in the piezoelectric transformer10-2 that are the same as those in the piezoelectric transformer 10 willbe omitted here.

A piezoelectric body 20-2 in the piezoelectric transformer 10-2 isdivided along the x-axis direction into seven equal regions, as shown inFIG. 10. The respective regions of the piezoelectric body 20-2 areindicated as polarized regions 21-2-23-2, a region 24-2, and polarizedregions 25-2-27-2, and are arranged in that order from a negative x-axisdirection side toward a positive x-axis direction side.

The polarized regions 21-2 and 27-2 are polarized in a directionparallel to the z-axis direction, as indicated by the arrows in FIG. 10.Specifically, a polarization direction 21-2 d of the polarized region21-2 and a polarization direction 27-2 d of the polarized region 27-2face the positive z-axis direction side.

The polarized regions 22-2, 23-2, 25-2, and 26-2 are polarized in adirection parallel to the x-axis direction, as indicated by the arrowsin FIG. 10. The polarization directions of adjacent polarized regionsare opposite from each other. Specifically, a polarization direction22-2 d of the polarized region 22-2 faces the negative x-axis directionside, and a polarization direction 23-2 d of the polarized region 23-2faces the positive x-axis direction side. Furthermore, a polarizationdirection 25-2 d of the polarized region 25-2 faces the negative x-axisdirection side, and a polarization direction 26-2 d of the polarizedregion 26-2 faces the positive x-axis direction side.

Unlike the region 24 in the piezoelectric transformer 10, the region24-2 is not polarized.

As shown in FIG. 10, an input electrode 30-2 in the piezoelectrictransformer 10-2 is a rectangular plate, and is provided so as to coverrespective surfaces of the region 24-2 on the positive z-axis directionside and the negative z-axis direction side thereof.

The output electrode in the piezoelectric transformer 10-2 is providedin two locations, in the polarized regions 21-2 and 27-2. The outputelectrode provided so as to cover the surface of the polarized region21-2 on the positive z-axis direction side thereof is referred to as anoutput electrode 40-2 a, and the output electrode provided so as tocover the surface of the polarized region 27-2 on the positive z-axisdirection side thereof is referred to as an output electrode 40-2 b. Thebasic configurations of the output outer electrodes, output innerelectrodes, and so on in the output electrodes 40-2 a and 40-2 b are thesame as in the output electrode 40, and thus descriptions thereof willbe omitted here.

The ground electrode in the piezoelectric transformer 10-2 is providedin two locations, in the polarized regions 21-2 and 27-2. The groundelectrode provided so as to cover the surface of the polarized region21-2 on the negative z-axis direction side thereof is referred to as aground electrode 50-2 a, and the ground electrode provided so as tocover the surface of the polarized region 27-2 on the negative z-axisdirection side thereof is referred to as a ground electrode 50-2 b. Thebasic configurations of the ground outer electrodes, the ground innerelectrodes, and so on in the ground electrodes 50-2 a and 50-2 b are thesame as in the ground electrode 50, and thus descriptions thereof willbe omitted here.

According to the piezoelectric transformer 10-2 configured as describedthus far, a segment sandwiched between the input electrode 30-2 and theground electrode 50-2 a, or in other words, the polarized regions 22-2and 23-2, functions as a driving portion. Likewise, a segment sandwichedbetween the input electrode 30-2 and the ground electrode 50-2 b, or inother words, the polarized regions 25-2 and 26-2, functions as a drivingportion. Furthermore, in the piezoelectric transformer 10-2, thepolarized regions 21-2 and 27-2 function as a power generating portion.

As shown in FIG. 10, in the piezoelectric transformer 10-2, the inputelectrode 30-2, the output electrodes 40-2 a and 40-2 b, and the groundelectrodes 50-2 a and 50-2 b are provided on respective surfaces of thepiezoelectric body 20-2 on the positive z-axis direction side and thenegative z-axis direction side thereof. The respective central areas ofthe input electrode 30-2, the output electrodes 40-2 a and 40-2 b, andthe ground electrodes 50-2 a and 50-2 b in the x-axis direction arelocated at nodes of the waveform W7, and thus do not easily vibrate. Asshown in FIG. 10, central areas of each electrode in the x-axisdirection are bonded to lead lines c1-c6 for connecting to an AC powersource, various types of electronic components, and so on; accordingly,the piezoelectric transformer 10-2 can prevent breakage at the locationsof the bonds between the lead lines and the corresponding electrodescaused by vibrations produced in the piezoelectric body 20-2.

(Third Variation)

Hereinafter, a piezoelectric transformer 10-3 according to a thirdvariation will be described with reference to the drawings. FIG. 11 isan external perspective view of the piezoelectric transformer 10-3according to the third variation, and is a diagram that also illustratespolarization directions at respective areas. The arrows in FIG. 11indicate the polarization directions. Note that descriptions ofconfigurations in the piezoelectric transformer 10-3 that are the sameas those in the piezoelectric transformer 10 will be omitted here.

A piezoelectric body 20-3 in the piezoelectric transformer 10-3 isdivided along the x-axis direction into seven equal polarized regions,as shown in FIG. 11. The polarized regions of the piezoelectric body20-3 are indicated as polarized regions 21-3-27-3, and are arranged inthat order from the negative x-axis direction side toward the positivex-axis direction side.

The polarized regions 21-3, 24-3, and 27-3 are polarized in a directionparallel to the z-axis direction, as indicated by the arrows in FIG. 11.Specifically, a polarization direction 21-3 d of the polarized region21-3 faces the positive z-axis direction side. Likewise, a polarizationdirection 24-3 d of the polarized region 24-3 faces the negative z-axisdirection side. Furthermore, a polarization direction 27-3 d of thepolarized region 27-3 faces the positive z-axis direction side.

The polarized regions 22-3, 23-3, 25-3, and 26-3 are polarized in adirection parallel to the x-axis direction, as indicated by the arrowsin FIG. 11. The polarization directions of adjacent polarized regionsare opposite from each other. Specifically, a polarization direction22-3 d of the polarized region 22-3 faces the negative x-axis directionside, and a polarization direction 23-3 d of the polarized region 23-3faces the positive x-axis direction side. Furthermore, a polarizationdirection 25-3 d of the polarized region 25-3 faces the negative x-axisdirection side, and a polarization direction 26-3 d of the polarizedregion 26-3 faces the positive x-axis direction side.

As shown in FIG. 11, the input electrode in the piezoelectrictransformer 10-3 is configured of an input electrode 30-3 provided at aborder between the polarized regions 22-3 and 23-3 and an inputelectrode 32-3 provided at a border between the polarized regions 25-3and 26-3. The input electrodes 30-3 and 32-3 are square plates that areparallel to a plane orthogonal to the x-axis direction.

As shown in FIG. 11, the output electrode in the piezoelectrictransformer 10-3 is provided in the polarized regions 21-3, 24-3, and27-3. The output electrode provided so as to cover the surface of thepolarized region 21-3 on the positive z-axis direction side thereof isreferred to as an output electrode 40-3 a, and the output electrodeprovided so as to cover the surface of the polarized region 24-3 on thepositive z-axis direction side thereof is referred to as an outputelectrode 40-3 b. Furthermore, the output electrode provided so as tocover the surface of the polarized region 27-3 on the positive z-axisdirection side thereof is referred to as an output electrode 40-3 c. Thebasic configurations of the output outer electrodes, output innerelectrodes, and so on in the output electrodes 40-3 a, 40-3 b, and 40-3c are the same as in the output electrode 40, and thus descriptionsthereof will be omitted here.

As shown in FIG. 11, a ground electrode 50-3 is provided in thepolarized regions 21-3, 24-3, and 27-3. The ground electrode provided soas to cover the surface of the polarized region 21-3 on the negativez-axis direction side thereof is referred to as a ground electrode 50-3a, and the ground electrode provided so as to cover the surface of thepolarized region 24-3 on the negative z-axis direction side thereof isreferred to as a ground electrode 50-3 b. Furthermore, the groundelectrode provided so as to cover the surface of the polarized region27-3 on the negative z-axis direction side thereof is referred to as aground electrode 50-3 c. The basic configurations of the ground outerelectrodes, the ground inner electrodes, and so on in the groundelectrodes 50-3 a, 50-3 b, and 50-3 c are the same as in the groundelectrode 50, and thus descriptions thereof will be omitted here.

Here, in the piezoelectric transformer 10-3, the polarized regions 22-3and 23-3 configure a driving portion 60-3, and the polarized regions25-3 and 26-3 configure a driving portion 62-3. Furthermore, thepolarized regions 21-3, 24-3, and 27-3 configure a power generatingportion 70-3.

The piezoelectric transformer 10-3 configured as described thus far canachieve a larger input electrostatic capacity than the piezoelectrictransformer 10 for the reasons described hereinafter.

An electrostatic capacity is formed between the input electrode 30-3 andthe ground electrode 50-3 a in the piezoelectric transformer 10-3. Adistance between the input electrode 30-3 and the ground electrode 50-3a is half the distance between the input electrode 30 and the groundelectrode 50 in the piezoelectric transformer 10. In other words, theelectrostatic capacity formed between the input electrode 30-3 and theground electrode 50-3 a is double the electrostatic capacity formedbetween the input electrode 30 and the ground electrode 50 in thepiezoelectric transformer 10. Furthermore, an electrostatic capacity isformed between the input electrode 30-3 and the ground electrode 50-3 bin the piezoelectric transformer 10-3. A distance between the inputelectrode 30-3 and the ground electrode 50-3 b is half the distancebetween the input electrode 30 and the ground electrode 50 in thepiezoelectric transformer 10. In other words, the electrostatic capacityformed between the input electrode 30-3 and the ground electrode 50-3 bis double the electrostatic capacity formed between the input electrode30 and the ground electrode 50 in the piezoelectric transformer 10.

Accordingly, the electrostatic capacity produced in the driving portion60-3 of the piezoelectric transformer 10-3 is quadruple theelectrostatic capacity in the driving portion 60 of the piezoelectrictransformer 10. The same applies to the electrostatic capacity producedin the driving portion 62-3. The piezoelectric transformer 10-3 cantherefore provide a higher input electrostatic capacity than thepiezoelectric transformer 10.

Other Embodiments

The piezoelectric transformer according to the present invention is notlimited to the piezoelectric transformer 10 and the piezoelectrictransformers 10-1, 10-2, and 10-3 that are variations thereon, and manymodifications can be made without departing from the essential scope ofthe present invention. For example, the piezoelectric transformer 10 maybe used as a step-up transformer by switching the input electrodes andthe output electrodes in the piezoelectric transformer 10. Thepiezoelectric transformer may also handle vibrations of a higher orderthan the seventh-order vibration mode. Furthermore, the direction inwhich the piezoelectric body 20 is layered may be parallel to the x-axisdirection, the y-axis direction, or the like.

As described thus far, the present invention is useful for apiezoelectric transformer used in contactless power transmission and thelike, and is particularly useful in terms of making it possible tosuppress unnecessary vibration modes from being produced.

REFERENCE SIGNS LIST

-   -   10, 10-1, 10-2, 10-3 piezoelectric transformer    -   20, 20-1, 20-2, 20-3 piezoelectric body    -   21-27, 23-1, 25-1, 21-2-23-2, 25-2-27-2, 21-3-27-3 polarized        region    -   30, 32, 30-2, 30-3, 32-3 input electrode    -   40, 40-1, 40-2 a, 40-2 b, 40-3 a, 40-3 b, 40-3 c output        electrode    -   60, 60-1, 60-3, 62, 62-1, 62-3 driving portion    -   70, 70-1, 70-3 power generating portion

The invention claimed is:
 1. A piezoelectric transformer comprising: apiezoelectric body having a plurality of polarized regions arranged in alengthwise direction of the piezoelectric body, the length of each ofthe polarized regions in the lengthwise direction being equal, a firstsubset of at least two of the plurality of polarized regions defining afirst driving portion, a second subset of at least two of the pluralityof regions defining a second driving portion and a third subset of theplurality of polarized regions defining a power generation portion; aninput electrode constructed to apply a voltage to the first and seconddriving portions; and an output electrode constructed to output avoltage generated by the power generating portion; the first and seconddriving portions being disposed symmetrically relative to a plane thatpasses through a center of the piezoelectric body in the lengthwisedirection and orthogonal to the lengthwise direction, and the pluralityof polarized regions defining the first and second driving portionsbeing no less than half of the plurality of polarized regions of thepiezoelectric body.
 2. The piezoelectric transformer according to claim1, wherein each of the polarized regions of the first and second drivingportions are polarized in the lengthwise direction.
 3. The piezoelectrictransformer according to claim 2, wherein at least two adjacentpolarized regions of at least one of the first and second drivingportions are polarized in opposite directions.
 4. The piezoelectrictransformer according to claim 1, wherein two adjacent polarized regionsof at least one of the first and second driving portions are polarizedin opposite directions.
 5. The piezoelectric transformer according toclaim 1, wherein the third subset of polarized regions comprises atleast two polarized regions and each of the polarized regions of thepower generation portion are polarized in a direction which isorthogonal to the lengthwise direction.
 6. The piezoelectric transformeraccording to claim 5, wherein each adjacent polarized region of thepower generating portion is polarized in a direction opposite itsadjacent polarized region of the power generating portion.
 7. Thepiezoelectric transformer according to claim 1, wherein the third subsetof polarized regions comprises at least two polarized regions and eachadjacent polarized region of the power generating portion is polarizedin a direction opposite to its adjacent polarized region of the powergenerating portion.
 8. The piezoelectric transformer according to claim1, further comprising: a ground electrode arranged such that a pluralityof polarized regions are between the input electrode and the groundelectrode.
 9. The piezoelectric transformer according to claim 1,wherein a cross-section of the piezoelectric body taken along adirection orthogonal to the lengthwise direction of the piezoelectricbody has a square shape.
 10. The piezoelectric transformer according toclaim 1, wherein a number of the plurality of polarized regions is anodd number.
 11. The piezoelectric transformer according to claim 1,wherein the input electrode comprises opposed input electrodes providedon respective opposed end surfaces of the piezoelectric body in thelengthwise direction.
 12. The piezoelectric transformer according toclaim 8, wherein the input electrode comprises opposed input electrodesprovided on respective opposed end surfaces of the piezoelectric body inthe lengthwise direction.
 13. The piezoelectric transformer according toclaim 12, wherein a first distance between each opposed input electrodeand the ground electrode is greater than a second distance between theoutput electrode and the ground electrode.
 14. The piezoelectrictransformer according to claim 1, wherein the input electrode isprovided in a central area of the piezoelectric body in the lengthwisedirection thereof.
 15. The piezoelectric transformer according to claim1, further comprising a non-polarized region in a central area of thepiezoelectric body in the lengthwise direction thereof, and wherein theinput electrode is provided in the non-polarized region.
 16. Thepiezoelectric transformer according to claim 1, wherein the inputelectrode comprises opposed input electrodes provided at a borderbetween adjacent polarized regions in each of the plurality of drivingportions.
 17. The piezoelectric transformer according to claim 1,wherein the plurality of polarized regions is seven and the phase of theseventh order vibration mode waveform advances by 180 degrees as itadvances from one adjacent polarized region to the next.